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This invention relates to arresting nets used to arrest travel of aircraft overrunning runways and, more particularly, to arrangements for frangibly securing arresting nets in position across a runway.
Aircraft arresting nets are used to arrest forward motion of aircraft. For example, an aircraft which, when landing, fails to stop before the end of an operative landing surface, creating an emergency situation. In addition to stopping the aircraft, objectives are to avoid injury to persons aboard the aircraft and avoid or minimize damage to the aircraft. To meet these objectives an arresting net (which is typically a composite of many net elements) is stretched across the end of a runway. Upper and lower horizontal straps supporting vertical straps are connected to energy absorbing mechanisms at the sides of the runway to decelerate and stop and aircraft. Form, construction and operation of arresting nets are described in the present inventor""s U.S. Pat. No. 4,979,701, issued Dec. 25, 1990, (the ""701 patent) which is hereby incorporated by reference herein.
For effective use, an arresting net must be stretched across a runway end, with vertical straps extended and with the lower edge of the net anchored in proper position to enable an aircraft to properly engage the net.
FIG. 1 shows an example of a prior net element (e.g., spread out on a flat surface). FIG. 2 is a simplified view of a composite arresting net as positioned across a runway and including an upper suspension cable and lower anchoring arrangement. The suspension cable and anchoring arrangement are employed to position the arresting net and to break upon aircraft impact with the net, so that the horizontal and vertical straps of the net engage and decelerate the aircraft. FIG. 3 provides a simplified spread view of fifteen individual net elements, which together may comprise the arresting net represented in FIG. 2.
As noted, it is desirable to anchor the arresting net to the runway when it is installed and positioned for emergency use as may be required. FIG. 4 illustrates a prior arrangement whereby each bottom strap of an arresting net is secured to a heavy anchor strap, shown lying on a runway surface, by an individual piece of lacing cord (e.g., light nylon line) which is knotted to remain in position. FIG. 5 shows further detail indicating how a D-ring at the end of the anchor strap is inserted into an anchor disk affixed to the runway surface and secured by insertion of a pin into the anchor disk and through the D-ring. An arresting net may, for example, utilize 17 anchor disk, anchor strap combinations at spaced positions across a runway, with each of two bottom straps of each of 15 net elements individually tied by lacing cord to each anchor strap. As indicated, upon aircraft impact the lacing cords break and the horizontal and vertical arresting net straps stop the aircraft under control of the energy absorbing mechanisms.
This use of lacing cord to anchor the lower arresting straps is effective in appropriate deployment of the arresting net. However, in this example net anchoring requires that 510 pieces of lacing cord be manually and individually positioned and tied. This effort, which may require 4 to 8 man-hours to complete, must be performed upon net installation, again following each aircraft arresting incident and possibly also on a routine preventive maintenance basis. In addition to this level of effort, proper installation and execution of each knot to specification (e.g., as to type and placement of cord and knot) and inspection thereof can be a matter of concern.
Accordingly, objects of the present invention are to provide new and improved anchoring systems for aircraft arresting nets, and such anchoring systems which may have one or more of the following characteristics and capabilities:
reliable net anchoring;
predetermined frangibility in arresting incidents;
ease of installation and replacement;
simplified, time effective installation;
durable reusable components; and
low cost expendable components.
In accordance with the invention, an anchoring system, to secure a member of an aircraft arresting net to a runway, may include a frangible anchor link, an elongated anchor element and an anchor retainer. The frangible anchor link, which may have the form of a strip of sheet plastic or other material, includes a central portion positionable at least partially around the net member and end portions each having at least one opening. The elongated anchor element, which may have the form of an anchor cable, has two ends and is positionable through each end portion of the anchor link via at least one opening therein. The anchor retainer is affixable to a runway to releasably secure the anchor element to the runway. The anchoring system may also include an anchor end-piece to releasably secure at least one end of the anchor element to the anchor retainer.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.